2. Arm SiP Services¶
This document enumerates and describes the Arm SiP (Silicon Provider) services.
SiP services are non-standard, platform-specific services offered by the silicon
implementer or platform provider. They are accessed via SMC
(“SMC calls”)
instruction executed from Exception Levels below EL3. SMC calls for SiP
services:
Follow SMC Calling Convention;
Use SMC function IDs that fall in the SiP range, which are
0xc2000000
-0xc200ffff
for 64-bit calls, and0x82000000
-0x8200ffff
for 32-bit calls.
The Arm SiP implementation offers the following services:
Performance Measurement Framework (PMF)
Execution State Switching service
DebugFS interface
Source definitions for Arm SiP service are located in the arm_sip_svc.h
header
file.
2.1. Performance Measurement Framework (PMF)¶
The Performance Measurement Framework allows callers to retrieve timestamps captured at various paths in TF-A execution.
2.2. Execution State Switching service¶
Execution State Switching service provides a mechanism for a non-secure lower
Exception Level (either EL2, or NS EL1 if EL2 isn’t implemented) to request to
switch its execution state (a.k.a. Register Width), either from AArch64 to
AArch32, or from AArch32 to AArch64, for the calling CPU. This service is only
available when Trusted Firmware-A (TF-A) is built for AArch64 (i.e. when build
option ARCH
is set to aarch64
).
2.2.1. ARM_SIP_SVC_EXE_STATE_SWITCH
¶
Arguments:
uint32_t Function ID
uint32_t PC hi
uint32_t PC lo
uint32_t Cookie hi
uint32_t Cookie lo
Return:
uint32_t
The function ID parameter must be 0x82000020
. It uniquely identifies the
Execution State Switching service being requested.
The parameters PC hi and PC lo defines upper and lower words, respectively, of the entry point (physical address) at which execution should start, after Execution State has been switched. When calling from AArch64, PC hi must be 0.
When execution starts at the supplied entry point after Execution State has been switched, the parameters Cookie hi and Cookie lo are passed in CPU registers 0 and 1, respectively. When calling from AArch64, Cookie hi must be 0.
This call can only be made on the primary CPU, before any secondaries were
brought up with CPU_ON
PSCI call. Otherwise, the call will always fail.
The effect of switching execution state is as if the Exception Level were
entered for the first time, following power on. This means CPU registers that
have a defined reset value by the Architecture will assume that value. Other
registers should not be expected to hold their values before the call was made.
CPU endianness, however, is preserved from the previous execution state. Note
that this switches the execution state of the calling CPU only. This is not a
substitute for PSCI SYSTEM_RESET
.
The service may return the following error codes:
STATE_SW_E_PARAM
: If any of the parameters were deemed invalid for a specific request.STATE_SW_E_DENIED
: If the call is not successful, or when TF-A is built for AArch32.
If the call is successful, the caller wouldn’t observe the SMC returning. Instead, execution starts at the supplied entry point, with the CPU registers 0 and 1 populated with the supplied Cookie hi and Cookie lo values, respectively.
2.3. DebugFS interface¶
The optional DebugFS interface is accessed through an SMC SiP service. Refer to the component documentation for details.
String parameters are passed through a shared buffer using a specific union:
union debugfs_parms {
struct {
char fname[MAX_PATH_LEN];
} open;
struct mount {
char srv[MAX_PATH_LEN];
char where[MAX_PATH_LEN];
char spec[MAX_PATH_LEN];
} mount;
struct {
char path[MAX_PATH_LEN];
dir_t dir;
} stat;
struct {
char oldpath[MAX_PATH_LEN];
char newpath[MAX_PATH_LEN];
} bind;
};
Format of the dir_t structure as such:
typedef struct {
char name[NAMELEN];
long length;
unsigned char mode;
unsigned char index;
unsigned char dev;
qid_t qid;
} dir_t;
Identifiers
SMC_OK |
0 |
SMC_UNK |
-1 |
DEBUGFS_E_INVALID_PARAMS |
-2 |
MOUNT |
0 |
CREATE |
1 |
OPEN |
2 |
CLOSE |
3 |
READ |
4 |
WRITE |
5 |
SEEK |
6 |
BIND |
7 |
STAT |
8 |
INIT |
10 |
VERSION |
11 |
2.3.1. MOUNT¶
2.3.1.1. Description¶
This operation mounts a blob of data pointed to by path stored in src, at filesystem location pointed to by path stored in where, using driver pointed to by path in spec.
2.3.1.2. Parameters¶
uint32_t |
FunctionID (0x82000030 / 0xC2000030) |
uint32_t |
|
2.3.1.3. Return values¶
int32_t |
w0 == SMC_OK on success w0 == DEBUGFS_E_INVALID_PARAMS if mount operation failed |
2.3.2. OPEN¶
2.3.2.1. Description¶
This operation opens the file path pointed to by fname.
2.3.2.2. Parameters¶
uint32_t |
FunctionID (0x82000030 / 0xC2000030) |
uint32_t |
|
uint32_t |
mode |
mode can be one of:
enum mode {
O_READ = 1 << 0,
O_WRITE = 1 << 1,
O_RDWR = 1 << 2,
O_BIND = 1 << 3,
O_DIR = 1 << 4,
O_STAT = 1 << 5
};
2.3.2.3. Return values¶
int32_t |
w0 == SMC_OK on success w0 == DEBUGFS_E_INVALID_PARAMS if open operation failed |
uint32_t |
w1: file descriptor id on success. |
2.3.3. CLOSE¶
2.3.3.1. Description¶
This operation closes a file described by a file descriptor obtained by a previous call to OPEN.
2.3.3.2. Parameters¶
uint32_t |
FunctionID (0x82000030 / 0xC2000030) |
uint32_t |
|
uint32_t |
File descriptor id returned by OPEN |
2.3.3.3. Return values¶
int32_t |
w0 == SMC_OK on success w0 == DEBUGFS_E_INVALID_PARAMS if close operation failed |
2.3.4. READ¶
2.3.4.1. Description¶
This operation reads a number of bytes from a file descriptor obtained by a previous call to OPEN.
2.3.4.2. Parameters¶
uint32_t |
FunctionID (0x82000030 / 0xC2000030) |
uint32_t |
|
uint32_t |
File descriptor id returned by OPEN |
uint32_t |
Number of bytes to read |
2.3.4.3. Return values¶
On success, the read data is retrieved from the shared buffer after the operation.
int32_t |
w0 == SMC_OK on success w0 == DEBUGFS_E_INVALID_PARAMS if read operation failed |
uint32_t |
w1: number of bytes read on success. |
2.3.5. SEEK¶
2.3.5.1. Description¶
Move file pointer for file described by given file descriptor of given offset related to whence.
2.3.5.2. Parameters¶
uint32_t |
FunctionID (0x82000030 / 0xC2000030) |
uint32_t |
|
uint32_t |
File descriptor id returned by OPEN |
sint32_t |
offset in the file relative to whence |
uint32_t |
whence |
whence can be one of:
KSEEK_SET |
0 |
KSEEK_CUR |
1 |
KSEEK_END |
2 |
2.3.5.3. Return values¶
int32_t |
w0 == SMC_OK on success w0 == DEBUGFS_E_INVALID_PARAMS if seek operation failed |
2.3.6. BIND¶
2.3.6.1. Description¶
Create a link from oldpath to newpath.
2.3.6.2. Parameters¶
uint32_t |
FunctionID (0x82000030 / 0xC2000030) |
uint32_t |
|
2.3.6.3. Return values¶
int32_t |
w0 == SMC_OK on success w0 == DEBUGFS_E_INVALID_PARAMS if bind operation failed |
2.3.7. STAT¶
2.3.7.1. Description¶
Perform a stat operation on provided file name and returns the directory entry statistics into dir.
2.3.7.2. Parameters¶
uint32_t |
FunctionID (0x82000030 / 0xC2000030) |
uint32_t |
|
2.3.7.3. Return values¶
int32_t |
w0 == SMC_OK on success w0 == DEBUGFS_E_INVALID_PARAMS if stat operation failed |
2.3.8. INIT¶
2.3.8.1. Description¶
Initial call to setup the shared exchange buffer. Notice if successful once, subsequent calls fail after a first initialization. The caller maps the same page frame in its virtual space and uses this buffer to exchange string parameters with filesystem primitives.
2.3.8.2. Parameters¶
uint32_t |
FunctionID (0x82000030 / 0xC2000030) |
uint32_t |
|
uint64_t |
Physical address of the shared buffer. |
2.3.8.3. Return values¶
int32_t |
w0 == SMC_OK on success w0 == DEBUGFS_E_INVALID_PARAMS if already initialized, or internal error occurred. |
2.3.9. VERSION¶
2.3.9.1. Description¶
Returns the debugfs interface version if implemented in TF-A.
2.3.9.2. Parameters¶
uint32_t |
FunctionID (0x82000030 / 0xC2000030) |
uint32_t |
|
2.3.9.3. Return values¶
int32_t |
w0 == SMC_OK on success w0 == SMC_UNK if interface is not implemented |
uint32_t |
w1: On success, debugfs interface version, 32 bits value with major version number in upper 16 bits and minor version in lower 16 bits. |
CREATE(1) and WRITE (5) command identifiers are unimplemented and return SMC_UNK.
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